We propose to work out a method for isolation of protein structural genes from higher organisms. It involves limited exonuclease digestion of DNA, hybridization with messenger RNA corresponding to the desired gene, and separation of DNA-RNA hybrids from other DNA. The DNA which was hybridized will be replicated in Escherichia coli to produce large quantities. This method will be used to isolate the silk fibroin gene with the DNA sequences adjacent to it in the genome of the silkworm, Bombyx mori. We will determine whether the gene can be transcribed and RNA from it translated in bacteria. We will map the DNA adjoining the fibroin gene by restriction endonuclease cleavage and examine if for repeated sequences by its rate of annealing. If any reiterated segments are found, their association with tissue-specific transcription will be tested. BIBLIOGRAPHIC REFERENCES: Studies on the Silk Fibroin Gene. John F. Morrow, John M. Wozney, and Argiris Efstratiadis. In Recombinant Molecules: Impact on Science and Society edited by R.F. Beers, Jr. and E. G. Bassett, Raven Press, New York, 1977, in press. Bacterial Plasmids Containing Silk Gene Sequences. John F. Morrow, Nancy T. Chang, John M. Wozney, Anne C. Richards and Argiris Efstratiadis. In Molecular Cloning of Recombinant DNA, edited by W. A. Scott, Academic Press, New York, 1977, in press.